1. Field of the Invention
The present invention relates to a multilayer substrate having a gallium nitride layer and a method for forming the same, and more particularly, to a multilayer substrate having a gallium nitride layer with a relatively greater thickness and a relatively larger area and a method for forming the same.
2. Description of Related Art
In recent years, power electronic having silicon are significantly used in components of electric ground vehicles such as converters or inverters. However, these electronic components have performance restricted by property of silicon, and thus need to be fabricated by other materials.
Gallium nitride (GaN) has better physical property than silicon, and can be further grown on a silicon substrate so as to lower fabrication cost. Therefore, gallium nitride is a potential material for forming electronic components in electric ground vehicles.
However, in the conventional art, a gallium nitride layer formed on a silicon substrate has cracks resulting from tensile stress which are disadvantageous to following applications. Further, when the thickness or area of the gallium nitride layer is increased, more cracks occur, such that it is difficult to form a gallium nitride layer with a greater thickness. In addition, since there is a lattice mismatch between a gallium nitride layer and a silicon substrate, defects easily occur in the gallium nitride layer. Therefore, the efficacy of electronic components having gallium nitrides cannot be improved. Specifically, the electronic component has leakage current, the restricted direct current characteristic and the restricted breakdown voltage due to the gallium nitride layer with less thickness and high defect density.
In “AlGaN—GaN HEMTs on patterned silicon (111) substrate”, IEEE Electron Device Letters vol. 3, No. 26, March 2005, Shou Jia et al. disclose an epitaxial structure, wherein trenches are formed on a silicon substrate by etching, a plurality of rectangular bumps are formed, and a gallium nitride layer is formed on each bump. The gallium nitride layer having a thickness of 1.5 μm is formed on a very small area (30 μm2).
In “Stress relaxation in the GaN/AlN multilayers grown on a mesh-patterned Si(111) substrate”, Journal of Applied Physics vol. 98, 2005, C. H. Chen et al. disclose that a GaN layer is formed on a silicon (111) substrate, and then multilayers of GaN/AlN/GaN/AlN/GaN/AlN are formed on the silicon (111) substrate. However, the thickness of the outmost gallium nitride layer is only 1 μm.
Further, in “Crack-Free InGaN/GaN Light Emitters on Si (111)” phys. stat. sol. vol. 1, No. 188, A. Dadgar et al. disclose that a patterned GaN layer is formed on a silicon (111) substrate, 15 pairs of AlGaN/GaN layers are formed on the substrate (111) substrate, and then a GaN layer is formed. Although the thickness of the resulting GaN layer is 3.61 μm, the area of the GaN layer is only 100 μm2.
Therefore, the gallium nitride layer has insufficent thickness for being used in electronic components in the prior art.
Accordingly, there is a need to develop a gallium nitride layer with a greater thickness, larger area and no cracks.